In a wood sample, the wood near the pith is the origin of branches (shown by knots). This area has low structural properties, tends to have high spiral angle, and is more prone to warp. Accordingly, knowing pith location relative to the lumber surface can be critical in warp prediction, knot size determination, and lumber grading. Currently, there are no simple ways to predict the pith location.
Its varied knot structure makes grading Southern Yellow Pine (SYP) lumber a challenge. Knots originate in the pith, so knowing the location of pith within a piece of lumber is required to estimate the size of its knots. Pith-containing and non-pith-containing lumber are well known to have contrasting wood properties. Pith containing lumber tends to be over-dried in the kiln, prone to warp, and has low mechanical properties. Juvenile wood is the wood surrounding the pith. Juvenile wood has high spiral angle, low density, high microfibril angle (MFA), and poor structural properties. The ability to identify the location of pith will improve knot volume assessment, lumber warp prediction, lumber drying, and strength grading of SYP and other species. Accurate estimation of the size of knots can also optimize the recovery of clear wood in remanufacturing.
Information of the approximate location of pith relative to the surface of lumber can be derived by comparing wane, knot count, knot size and shape, and the grain swirling pattern around a knot between the sides and between the edges of a piece of lumber. Such methods are applicable only when there are knots on opposite sides of the lumber. Pith location also can be identified using end scanning techniques; however, the pith locations are interpolated from only two end points.
Accordingly, a need exists for methods for more efficient detection of pith location and direction relative to lumber along a length of the lumber.